Five juvenile copepodids of Critomolgus anthopleurus Kim, 1996, were obtained by rearing the copepod and its actiniarian host for 10 days within a laboratory aquarium. Copepodid I of C. anthopleurus shows significant morphological differences from previous records. At this stage of C. anthopleurus, the antennule is 4-segmented, with 3 setae on the first segment; the antenna has a rudimentary exopod; the mandible has 2 armature elements in addition to distal lash; and the maxilliped is 4-segmented, with an armature formula 1, 2, 1, and 3. Sexual dimorphism first occurs at copepodid V of the maxilliped, which differs between sexes. A comparison of the maxillipeds of copepodid I between C. anthopleurus and other lichomolgoid copepods resulted in a conclusion that the maxillipedal endopod of the lichomolgoid copepodid I is fundamentally 2-segmented, with 1 seta on the first segment, and 3 setae and a setiform process on the second segment.